ESDU Aero W.01.01.04 presents curves of the ratio of the wing or tailplane lift-curve slope with cut-out to that without cut-out plotted against cut-out span as a fraction of wing or tailplane span for various values of cut-out chord as a fraction of wing or tailplane chord. A sketch indicates how the span and chord of the cut-out are defined. The curves are theoretically derived for a rectangular cut-out.